Contribution of the root system to the flowering process remains poorly studied. Part of the problem resides in its difficult isolation from the substrate, especially on adult plants. Taking advantage of ... [more ▼]

Contribution of the root system to the flowering process remains poorly studied. Part of the problem resides in its difficult isolation from the substrate, especially on adult plants. Taking advantage of an hydroponic device that allows synchronous growth and flowering of Arabidopsis thaliana (Tocquin et al., 2003), we performed global transcript profiling of roots during induction of flowering by a single long day (LD). Results were validated by real-time RT-PCR, and the expression patterns of selected probes were further analyzed in shoots and roots. Some of the genes that were identified in the microarray experiment were already known to be involved in the photoperiodic pathway of flowering in Arabidopsis, and hence were activated in both roots and shoots during the LD. These genes include, for example, components of light signaling or circadian machinery (e.g. GIGANTEA). Other genes providing new insights into the control of flowering at the whole plant level will be presented. Tocquin et al., (2003). BMC Plant Biology, 3: 2. [less ▲]

Vernalization is known to promote flowering in Arabidopsis thaliana by inhibiting the expression of a strong repressor: FLOWERING LOCUS C (FLC). The recent cloning of an FLC-LIKE gene in sugar beet (Beta ... [more ▼]

Vernalization is known to promote flowering in Arabidopsis thaliana by inhibiting the expression of a strong repressor: FLOWERING LOCUS C (FLC). The recent cloning of an FLC-LIKE gene in sugar beet (Beta vulgaris; BvFL1) and – here – in root chicory (Cichorium intybus; CiFL1) suggests the conservation of FLC biological function during evolution of eudicots. Hence physiological questions that remain difficult to address in Arabidopsis can be studied in other species. We investigated the correlation between CiFL1 expression and plant-age dependent responsiveness to vernalization. We also studied the effect of post-vernalization growing temperature, which can stabilize or erase the vernalized state. [less ▲]

Molecular genetic analyses in Arabidopsis disclosed a genetic pathway whereby flowering is induced by the photoperiod. This cascade is examined here within the time course of floral transition in the long ... [more ▼]

Molecular genetic analyses in Arabidopsis disclosed a genetic pathway whereby flowering is induced by the photoperiod. This cascade is examined here within the time course of floral transition in the long-day (LD) plant Sinapis alba induced by a single photoperiodic cycle. In addition to previously available sequences, the cloning of CONSTANS (SaCO) and FLOWERING LOCUS T (SaFT) homologues allowed expression analyses to be performed to follow the flowering process step by step. A diurnal rhythm in SaCO expression in the leaves was observed and transcripts of SaFT were detected when light was given in phase with SaCO kinetics only. This occurred when day length was extended or when a short day was shifted towards a ‘photophile phase’. The steady-state level of SaFT transcripts in the various physiological situations examined was found to correlate like a rheostat with floral induction strength. Kinetics of SaFT activation were also consistent with previous estimations of translocation of florigen out of leaves, which could actually occur after the inductive cycle. In response to one 22-h LD, initiation of floral meristems by the shoot apical meristem (SAM) started about 2 days after activation of SaFT and was marked by expression of APETALA1 (SaAP1). Meanwhile, LEAFY (SaLFY) was first up-regulated in leaf primordia and in the SAM. FRUITFULL (SaFUL) was later activated in the whole SAM but excluded from floral meristems. These patterns are integrated with previous observations concerning upregulation of SUPPRESSOR OF OVEREXPRESSION OF CO1 (SaSOC1) to provide a temporal and spatial map of floral transition in Sinapis. [less ▲]

Vernalization is known to promote flowering in Arabidopsis via the repression by cold of the floral inhibitor gene FLOWERING LOCUS C (FLC). For long, FLC homologs have been found in Brassicaceae only but ... [more ▼]

Vernalization is known to promote flowering in Arabidopsis via the repression by cold of the floral inhibitor gene FLOWERING LOCUS C (FLC). For long, FLC homologs have been found in Brassicaceae only but it was recently reported that in sugar beet, the FLC-like gene BvFL1 functions as a repressor of flowering and is downregulated in response to cold. We describe here the cloning of CiFL1 from root chicory (Cichorium intybus). Expression patterns were studied in two cultivars, differing in their sensitivity to vernalization. Transcript level analyzes were performed during the vernalization treatment of the seedlings and in different post-vernalization conditions. Our results give further support to conservation of the biological function of FLC-like genes in eudicot species. [less ▲]

Flowering time in plants is controlled by a number of environmental factors, among which photoperiod plays a key role. Maize ancestors are short-day (SD) plants, but breeding programs have selected ... [more ▼]

Flowering time in plants is controlled by a number of environmental factors, among which photoperiod plays a key role. Maize ancestors are short-day (SD) plants, but breeding programs have selected genotypes whose flowering is largely autonomous and occurs after production of a constant number of leaves regardless of photoperiod. Only few flowering time genes have been identified in maize; one of them is INDETERMINATE1 (ID1), cloned from a late-flowering mutant and encoding a zinc finger transcription factor. By contrast, the genetical control of flowering by photoperiod is best understood in the long-day (LD) dicot Arabidopsis and the SD monocot rice. A key regulator is the CONSTANS gene that mediates between the circadian clock – the time-keeper of the plant – and the synthesis of flowering signals. Here we report the analysis of a CONSTANS homolog in maize, ZmCO, in SD and in LD, and in different parts of the plant. Expression of ZmCO was found to be rhythmic and to be much higher in young leaf primordia than in mature leaf blades. Striking coincidence was observed with expression of ID1. [less ▲]

Eukaryotic phosphomannomutases (PMMs) catalyze the interconversion of mannose 6-phosphate to mannose 1-phosphate and are essential to the biosynthesis of GDP-mannose. As such, plant PMMs are involved in ... [more ▼]

Eukaryotic phosphomannomutases (PMMs) catalyze the interconversion of mannose 6-phosphate to mannose 1-phosphate and are essential to the biosynthesis of GDP-mannose. As such, plant PMMs are involved in ascorbic acid (AsA) biosynthesis and N-glycosylation. We report on the conditional phenotype of the temperature-sensitive Arabidopsis thaliana pmm-12 mutant. Mutant seedlings were phenotypically similar to wild type seedlings when grown at 16-18 degrees C but died within several days after transfer to 28 degrees C. This phenotype was observed throughout both vegetative and reproductive development. Protein extracts derived from pmm-12 plants had lower PMM protein and enzyme activity levels. In vitro biochemical analysis of recombinant proteins showed that the mutant PMM protein was compromised in its catalytic efficiency (K cat/K m). Despite significantly decreased AsA levels in pmm-12 plants, AsA deficiency could not account for the observed phenotype. Since, at restrictive temperature, total glycoprotein patterns were altered and glycosylation of protein-disulfide isomerase was perturbed, we propose that a deficiency in protein glycosylation is responsible for the observed cell death phenotype. [less ▲]